1. Field of the Invention
The present invention relates to a semiconductor device and a method for manufacturing the semiconductor device.
2. Description of the Related Art
Nonvolatile semiconductor memory devices using, as a charge-storage layer, a charge-storage insulating film in which charges can be trapped have been proposed (see, for example, Jpn. Pat. Appln. KOKAI Publication No. 2004-158810). The charge-trap nonvolatile semiconductor memory device traps charges injected into the charge-storage insulating film through a tunnel insulating film, in a trap state in the charge-storage insulating film. The charges are thus stored in the charge-storage insulating film. Known typical charge-trap nonvolatile semiconductor memory devices are of a MONOS or SONOS type.
To neutralize charges in the charge-trap nonvolatile semiconductor memory device, the erase characteristics need to be improved by effectively injecting holes into the charge-storage insulating film. Thus, a structure has been proposed which uses a stacked film of a silicon oxide film, a silicon nitride film, and a silicon oxide film as a tunnel insulating film (see, for example, Jpn. Pat. Appln. KOKAI Publication No. 2006-216215). However, the resulting tunnel insulating film may not be optimum.